1. Field of the Invention
The present invention relates to a breather system for a general-purpose four-cycle engine mounted in a work machine such as a construction machine or an earth moving machine, and in particular to an improvement of an engine breather system.
2. Description of Related Art
Conventional engine breather systems, such as the one disclosed in Japanese Patent Application Laid-open No. 62-240413, teach that the one-way valve works to maintain the pressure of the crank chamber appropriately so that breather gas flows from the first breather chamber to the intake system via the second breather chamber only when the pressure of the crank chamber increases.
A work machine, such as a rammer, might be positioned at an orientation (attitude) different from its normal standing orientation during operation due to operating error, unstable ground, etc. If the operation of the engine is continued in such an irregular orientation in the conventional arrangement, the oil within the crankcase might leak into the intake system. The first breather chamber is filled with oil so that the oil level is above the open end on the first breather chamber side of the communicating passage connecting the first and second breather chambers. Assuming the first breather chamber is below the second breather chamber, the one-way valve remains closed when the crank chamber has a negative pressure, although the negative pressure works on the first and second breather chambers. When the crank chamber has a positive pressure, since the oil within the communicating passage ascends within the communicating passage while opening the one-way valve by the action of the positive pressure imposed on the first and second breather chambers, continued operation of the engine makes the oil ascend within the communicating passage and supplies the oil to the second breather chamber. This creates the possibility that the oil within the second breather chamber will leak into the intake system.
The present invention has been carried out in view of the above circumstances It is an object of the present invention to provide an engine breather system that prevents oil from leaking into an intake system accompanying continuous operation of an engine in an attitude different from a normal attitude.
In order to achieve the object above, the present invention provides an engine breather system that includes a first breather chamber communicating with a crank chamber formed within a crankcase and a second breather chamber communicating with the crank chamber as well as with an intake system. The engine breather system also includes a communicating passage connecting the first and second breather chambers, and a one-way valve provided at an open end, on the second breather chamber side of the communicating passage so as to prevent breather gas from flowing from the second breather chamber toward the first breather chamber, wherein the one-way valve is provided with a pressure relief hole.
In accordance with this arrangement, in the case where operation of the engine is continued in a state in which the first breather chamber is below the second breather chamber, the first breather chamber being filled with oil so that the oil level is above the open end, on the first breather chamber side, of the communicating passage, when the crank chamber has a negative pressure, the upper space above the oil surface within the communicating passage communicates with the second breather chamber due to the pressure relief hole provided in the one-way valve in spite of the one-way valve being closed. Therefore, the oil level within the communicating passage decreases. The oil level within the communicating passage thus only repeatedly increases and decreases when operation of the engine is continued. Also, the oil is not pushed up toward the second breather chamber, thereby preventing the oil from leaking into the intake system.
Modes for carrying out the present invention are explained below by reference to an embodiment of the present invention shown in the attached drawings.